Magnetoresistive random access memory (MRAM) is one of several new types of random access memory in development that would likely serve as alternatives to the mainstream flash memory design. It maintains a nonvolatile status while retaining the attributes of high speed of reading and writing, high density of capacity, and low consumption of power. The core technology difference between MRAM and other types of nonvolatile random access memory is the method in which it defines and stores digital bits as different magnetic states. Thin magnetic films are stacked in a structure called a magnetic tunnel junction (MTJ) in which the resistance of the MTJ is defined by the relative directions of the magnetic films: parallel or anti-parallel. The variation in electrical current that passes through the two alternating magnetic states of this MTJ structure defines the digital bits (“0” and “1”) for MRAM. The memory bit element can be programmed by a magnetic field created from pulse-current-carrying conductors above and below the junction structure. In a newer design of MRAM, a spin transfer switching technique can be used to manipulate the memory element as well. This new design will allow better packing and shrinkage of individual MTJ devices on the wafer, effectively increasing the overall density of the MRAM memory elements.
MRAM devices are often combined with complementary metal-oxide-semiconductor (CMOS) devices. Process integration involves connection between MRAM and CMOS elements without causing any defect related issues.
U.S. Pat. No. 7,884,433 to Zhong et al and U.S. Patent Application 2011/0089507 to Mao, assigned to the same assignee as the present disclosure, and herein incorporated by reference in their entirety, teach methods of MRAM and CMOS integration. U.S. Pat. No. 7,705,340 to Lin discloses MRAM and CMOS devices. U.S. Pat. Nos. 6,809,951 to Yamaguchi and 6,246,082 to Mitarai et al disclose aluminum bit lines.